1. Field of the Invention
The present invention relates to a toner for developing latent electrostatic images, an electrostatic charge image developer for developing latent electrostatic images, a toner container, an image forming device, and an image forming method which are applied to electrophotographic methods, electrostatic recording methods, electrostatic printing methods, and the like.
2. Description of the Related Art
Conventionally, a large number of methods, such as those in U.S. Pat. No. 2,297,691, Japanese Patent Application Publication (JP-B) No. 42-23910 (U.S. Pat. No. 3,666,363), JP-B No. 43-24748 (U.S. Pat. No. 4,071,361), and the like have been disclosed as electrophotographic methods. Generally, a latent electrostatic image is formed on an image carrier such as a photosensitive body or the like by various means. Next, the obtained latent electrostatic image is developed by using a toner. Further, as needed, after the toner is transferred onto a transfer material such as paper or the like, the toner is fused by heating, application of pressure, evaporating the solvent, or the like. On the other hand, the toner which remains on the image carrier without being transferred is cleaned. In this way, copy images are repeatedly obtained.
There are various types of developing methods for making a latent electrostatic image visible by using toner. Such methods are broadly classified into dry developing methods and wet developing methods.
Dry developing methods are further classified into methods utilizing double-component electrostatic charge image developers formed from a toner and a carrier, and methods utilizing a single-component electrostatic charge image developer formed from toner alone. The single-component electrostatic charge image developers are classified into magnetic single-component electrostatic charge image developers which utilize magnetic materials, and non-magnetic single-component electrostatic charge image developers which do not utilize magnetic materials. Currently, developing methods utilizing double-component electrostatic charge image developers are mainly used, from the standpoints of superior high speed properties, stability, and the like.
In a method utilizing a double-component electrostatic charge image developer, by stirring and rubbing the toner and the carrier, the toner and the carrier are charged to respectively different polarities, and a latent electrostatic image having a polarity which is opposite that of the charged toner is made visible. In accordance with the types of the toners and carriers, a magnetic brush developing method using an iron powder carrier (disclosed in U.S. Pat. No. 2,874,063), a cascade method using a beads carrier (disclosed in U.S. Pat. No. 2,618,552), a fur brush method, and the like are known. Further, as a black toner which is applied to these various types of developing methods, a fine powder is used in which a coloring agent such as carbon black or the like is dispersed in a binder resin formed from a synthetic resin or a natural resin.
Hereinafter, a developing method using a double-component electrostatic charge image developer will be described.
When a large number of copies are continuously output by using a double-component electrostatic charge image developer, at first, clear, good image quality can be obtained. However, gradually, replenishment of toner to the electrostatic charge image developer is not in time and the image quality deteriorates, or the replenished toner and the carrier are mixed together in a state in which charging is insufficient. In this way, toner deposition of the background of images, toner scattering and the like easily occurs. Places arise on portions of the developing sleeve where the toner is thin, and the tendency toward image blurring, non-uniform image density and the like can be seen. Such problems are marked particularly when images of large image surface areas are continuously output. Further, these phenomena tend to arise easily particularly with toners in which carbon black is utilized in the coloring agent.
Carbon black, which is generally used as a coloring agent, is an electrically conductive substance and is a high dielectric. Thus, in cases in which carbon black is dispersed within or included in the toner, the electrical conductivity of the toner itself increases, and the resistance thereof decreases. Thus, toner deposition of the background of images, toner scattering and the like arise easily, causes the toner to easily receive effects, such as the injection of charges, the release of charges and the like, of an external electrical field. As a result, although the rise in the charging is good, the release of charges is rapid, and the chargeability deteriorates over time. The durability easily deteriorates, and the transferability tends to worsen.
Carbon black forms secondary cohered matter which are usually called agglomerates. The agglomerates must be dispersed uniformly to the primary particles. However, in actuality, dispersing to the primary particles is difficult. Usually, the agglomerates exist within the toner as primary cohered matter, which are called aggregates, or in a state similar thereto. Thus, the dispersability cannot be considered to be sufficient. It is thereby easy for the amount of charge to become non-uniform, and there is the tendency for toner deposition of the background of images and toner scattering to easily occur.
Methods have been proposed for carrying out an oxidation treatment on the surface of the carbon black to increase the resistivity of the carbon black.
Specifically, for example, JP-B No. 5-31139 discloses, as a surface oxidation treatment method, a method of oxidation treatment by potassium permanganate. However, in this method, metal ions tend to remain as counter ions of the carboxyl group on the surface of the carbon black, and the resistivity of the carbon black decreases. When used in a toner, sufficient effects relating to an improvement in durability in high humidity cannot be obtained.
Further, Japanese Patent Application Laid-Open (JP-A) No. 3-200158 discloses a surface oxidation treatment method by ozone. However, the object is the improvement of the dispersability of the carbon black by the mutual operation of the carboxyl group on the surface and polyester which is a binder resin for the toner. As for the degree of oxidation, the amount of carboxyl groups on the surface of the carbon black is less than 0.1xc3x9710xe2x88x923 mol/g, which is not very large. This is insufficient with respect to an improvement in the durability of the toner under high humidity.
On the other hand, among single-component electrostatic charge image developers, magnetic single-component electrostatic charge image developers which contain magnetic materials instead of carbon black are widely used. A magnetic single-component electrostatic charge image developer generally contains magnetic materials in an amount of 20 to 60% by weight, which is large. The saturation magnetization of the toner is around 10 to 50 emu/g which is large. The toner also has the characteristic that the true specific gravity is around 1.6 to 2.2 g/cm3 which is large, in contrast with the true specific gravity of about 1.2 to 1.3 g/cm3 of a toner using carbon black which does not contain magnetic materials. However, when such a toner is used as a toner for a double-component electrostatic charge image developer, the magnetic constraining force with respect to the carrier or the electrostatic charge image developer carrier or the like increases. Thus, the image density decreases, and it becomes difficult for the toner to separate from the surface of the carrier. As a result, there is a problem in that the toner easily fuses to the carrier surface, and so-called carrier spent easily occurs.
Accompanying the sudden popularization in recent years of OA machines such as copiers, printers, facsimile devices and the likes using electrophotographic methods, demands have increased for image quality, reproducibility and the like which are better than those which have been obtained conventionally. Further, by making the diameter of toner particles smaller, improvements in image quality are frequently achieved.
Although making the particle diameter of a toner smaller is effective in improving image quality, the smaller the toner particle diameter, the worse the dispersability of the respective structural components of the toner. This is a cause of the charge amount distribution of the toner becoming uneven and broad, there being an increase in toner adhering to the non-image portions on the photosensitive body, and there being an increase in toner deposition of the background of images.
Further, the smaller the toner particle diameter, the greater the cohesion of the toner. The fluidity thereby deteriorates, and problems arise in that filming and the like on the photosensitive body occur easily and stable image quality cannot be obtained over a long period of time. This trend is particularly marked in cases in which carbon black is used as the coloring agent of the toner and an image forming device is used which recycles cleaned toner in the developing section.
Next, the color developing method will be described.
Copies which have been obtained by electrophotographic methods to date are generally single color. However, recently, the requirements and demands for color copies have increased. Currently, there is the trend to use, as electrostatic charge image developers for obtaining quality color copies, dry-type double-component color electrostatic charge image developers which are generally formed from a carrier and a toner of a small particle diameter.
With dry-type double-component color electrostatic charge image developers, at the toner which has a small particle diameter, the amount of charge per toner particle (hereinafter called xe2x80x9cQ/Mxe2x80x9d upon occasion) is small. Thus, as the developing sleeve rotates, the toner easily scatters within the developing device. Further, in accordance therewith, scattering of the toner onto the image carrier becomes marked and appears as toner deposition of the background of images on the copies, and the quality of the copies therefore deteriorates. In particular, with color electrostatic charge image developers, it is said that if the toner density is not high as compared with that of monochrome electrostatic charge image developers, impressive images cannot be obtained. Accordingly, it is currently the situation that toners are used with the toner density thereof being set to be sufficiently high. However, an increase in the toner density is that much more disadvantageous in terms of toner scattering. To date, sufficient measures to counter toner scattering have not been taken. In a dry-type double-component color developing device, among the electrostatic charge image developers of the four colors of yellow, magenta, cyan, and black, carbon black, which is generally used as the coloring agent in the black electrostatic charge image developer, is an electrically conductive substance, and the electrical resistance thereof is low. When carbon black is dispersed within or contained in a toner, the electrical conductivity of the toner itself increases, and the chargeability deteriorates. Problems arise in that the toner deposition of the background of images and toner scattering easily occurs. Further, among the electrostatic charge image developers of the four colors, the amount of the black electrostatic charge image developer which is used is markedly high. Thus, among the above-described problems relating to toner scattering, scattering of black toner is a particularly great problem.
To address this problem, various solutions have been proposed such as including magnetic fine particles in the toner (JP-A No. 2-22673, JP-A No. 2-87158, and the like), making the color of the magnetic materials in the toners of the respective colors match the colors of the coloring agents in the toners of the respective colors so that the color characteristics do not change (so that hue offset does not occur) (JP-A No. 2-877, JP-A No. 2-207275, and the like), and the like.
Hereinafter, a developing method using a single-component electrostatic charge image developer will be described.
In recent years, as methods of developing latent electrostatic images by electrophotographic methods, electrostatic recording methods and the like, methods have become popular in which a developing magnet roller, which has a sleeve provided with a magnetic field generating means in the interior thereof, and a magnetic single-component toner are used in combination. Generally, the operation of developing a latent electrostatic image by a method using a magnetic single-component toner is carried out by rotating the sleeve, or rotating the magnet within the sleeve, or rotating both. Usually, developing is carried out by rotating the magnet. However, at this time, the rotational speed of the sleeve or the magnet is selected such that the moving speed of the magnetic toner is set to be 2 to 4 times that of the latent electrostatic image so that the pitch of the poles does not appear in the image. Thus, if an attempt is to be made to sufficiently ensure the uniformity of the image density, the rotation of the magnet must be made to be considerably fast, and a strong motor is required for this driving. This of course leads to the device becoming larger sized.
In order to overcome this drawback, a single-component electrostatic charge image developer which is not magnetic is disclosed in JP-B No. 41-9475. Here, a toner member having a thin layer of toner on the surface thereof is set in proximity with a latent electrostatic image forming body, and in light of the non-contact relationship thereof, the toner is made to fly onto only the latent electrostatic image. In this publication, the carrying of the toner is achieved by causing the toner to be attracted to and adsorbed at a web which is provided with an appropriate tackiness or a filmsheet to which charges have been given in advance. However, in this method, there are limits to the length of the sheet and the web, and this method is not suited for continuous copying or printing.
To overcome these problems, JP-A No. 60-229065 discloses a method in which a carrier for developing latent electrostatic images is made to be in an endless form, developing is carried out by the flying of a non-magnetic single-component toner, and the image is transferred onto a recording sheet. In this example, a uniformizing member is made to abut the developing roller such that a thin layer of toner is formed, and a developing bias such as a DC-superimposed AC or the like is applied such that the latent electrostatic image is developed. JP-A No. 50-30537 discloses a method of improving the image density by a pulse bias method. Further, JP-A No. 47-12635 and JP-A No. 50-10143 disclose structures of developing agent carriers having a fine pattern of insulator portions (dielectric portions) and electric conductor portions on the surface thereof. By using such fine electric fields, mountains and valleys of toners are formed in correspondence with the fine pattern, and toner is caused to adhere in correspondence with the electric potential levels of the latent electrostatic image, so as to aim for multilayering. In either method, the amount of electrostatic charge image developer on the latent electrostatic image carrier varies in accordance with the state in which the toner is applied onto the developing roller. Thus, the characteristics of the toner on the developing roller are important.
JP-A No. 58-116559 discloses various types of non-magnetic single-component developing methods which do not use carriers. With toners requiring a low melting point and sharp melting, if an external additive is caused to adhere to the toner surface for the purpose of improving the fluidity, by using a developing unit, the external additive is subjected to mechanical hazards such as at the time when the toner passes on a developing roller or a developer for latent electrostatic images applying blade or the like, and sinks into the toner surface. Thus, the characteristics of the toner on the developing roller are easily changed. In particular, a fluidity improving agent, which is applied externally for the purpose of improving the fluidity of the toner, causes changes in the toner characteristics by sinking into the toner surface. Thus, as before, there are problems to be solved such as stabilizing the amount of charge of the toner on the developing roller over time, stably ensuring a sufficient amount of electrostatic charge image developer to the latent electrostatic image carrier, preventing fogging of the background portions on the image, and the like.
A toner which is used in such a non-magnetic single-component developing method is a toner in which a coloring agent and the like are dispersed in a binder resin. Carbon black has been effectively used as a general, non-magnetic, black coloring agent. However, due to the structure thereof, carbon black has an electrical conductivity imparting effect. In particular, when a large amount of carbon black is used for the purpose of raising the degree of coloring, the electrical resistance of the toner decreases, and the charge retaining ability deteriorates. Thus, the chargeability deteriorates, and the amount of inversely-charged toner or lightly-charged toner which exists increases. Problems such as the scattering of toner, the so-called dirtying of background portions in which toner particles are developed on places other than the image portion where the latent electrostatic image is formed, and the like, can be seen, and there are limits on the amount of carbon black which can be contained. In particular, when the charge donating effect of the charge donating member weakens over time, insufficiently charged or weakly charged toner tinged with an inverse charge easily generates. Thus, such phenomena become marked.
In recent years, the demand on the market for images of high quality has increased. With toners having a conventional volume average particle diameter of 10 to 15 xcexcm, a sufficiently high image quality cannot be obtained, and toners of even smaller particle diameters are required. However, as the trend toward making the toner particle diameter smaller advances, various problems tend to arise. In particular, because the adhesive property of the toner itself is strengthened, charge donating member and the like easily become dirty by the toner. Charge donating ability of the charge donating member easily deteriorates over time, and there is less leeway with respect to toner deposition of the background of images and toner scattering.
The object of the present invention is to provide a toner for developing latent electrostatic images, a developer for latent electrostatic images, a container containing toner, an image forming device, and an image forming method which overcome the above-described problems of the prior art, and in which, in particular, even if a large number of images of large image areas are output continuously, toner deposition of the background of images and toner scattering and the like do not occur, and which have excellent fluidity, and in which filming and the like do not occur, and in which, even if a small particle diameter toner is used, it is possible to obtain stable image quality over a long period of time.
As the result of intensive investigation, the inventors of the present invention arrived at a first aspect of the present invention by discovering that, by using, as a toner for a single-component electrostatic charge image developer or a toner for a double-component electrostatic charge image developer, a toner which contains in a binder resin at least a coloring agent formed from a metal material, and which satisfies the relationships that the saturation magnetization is 0.01 to 10 emu/g and the true specific gravity is 1.33 to 1.62 g/cm3, even when a large number of images having large image surface areas are continuously output, toner deposition of the background of images, toner scattering and the like do not occur, the fluidity is excellent, there is little filming or the like, and even when a small particle diameter toner is used, stable image quality can be obtained over a long period of time.
Such a toner, which is weakly-magnetic and is almost non-magnetic and which has a true specific gravity which is near to that of a toner using a conventional carbon black, has not existed heretofore.
In a second aspect of the present invention, there is provided a container containing toner in which a toner for developing latent electrostatic images is housed in a toner container, the toner containing, in a binder resin, at least a coloring agent formed from a metal material, a saturation magnetization of the toner being 0.01 to 10 emu/g, and a true specific gravity of the toner being 1.33 to 1.62 g/cm3.
In a third aspect of the present invention, there is provided a developer for a latent electrostatic image comprising at least a toner for developing latent electrostatic images, the toner containing, in a binder resin, at least a coloring agent formed from a metal material, a saturation magnetization of the toner being 0.01 to 10 emu/g, and a true specific gravity of the toner being 1.33 to 1.62 g/cm3.
A fourth aspect of the present invention an image forming method comprising a latent electrostatic image forming step of forming a latent electrostatic image on a latent electrostatic image carrier; and a developing step of developing the electrostatic latent image by using an electrostatic charge image developer housed in a developing device, the electrostatic charge image developer containing at least a toner for developing latent electrostatic images, the toner containing, in a binder resin, at least a coloring agent formed from a metal material, a saturation magnetization of the toner being 0.01 to 10 emu/g, and a true specific gravity of the toner being 1.33 to 1.62 g/cm3.
Finally, a fifth aspect of the present invention provides an image forming device comprising a latent electrostatic image carrier; a latent electrostatic image forming means for forming a latent electrostatic image on the electrostatic latent image carrier; and developing means for housing an electrostatic charge image developer containing at least a toner for developing latent electrostatic images, the toner containing, in a binder resin, at least a coloring agent formed from a metal material, a saturation magnetization of the toner being 0.01 to 10 emu/g, and a true specific gravity of the toner being 1.33 to 1.62 g/cm3, and for developing the electrostatic latent image.